1. Field of the Invention
This invention relates, generally, to solid state load protection systems and more particularly to loss of phase sensing enabling the system to detect a loss of phase in a polyphase alternating current system thereby causing a trip signal to be generated so as to deenergize a load.
2. Description of the Prior Art
It is known that some load protection systems have various protection functions such as current overload, phase loss, and ground fault sensing. These functions generally provide a trip time for a circuit breaker and associated load which is inversely related to the square of the current flowing in the load to be protected. Therefore, an inverse time relationship is generally utilized whereby the time between a fault which is sensed and trip out are inversely related such that a high overcurrent will result in a very short period of time for device trip out and a relatively low overcurrent fault will result in a substantially longer time before trip out. Types of devices which accomplish the above can be found in U.S. Pat. No. 4,021,703, "Phase Imbalance Detection Circuit", issued May 3, 1977 to Gary, et al; U.S. Pat. No. 3,996,499, "Zener Diode Effect on Long Acceleration Module", issued Dec. 7, 1976 to Gary, et al.; U.S. Pat. No. 3,818,275, "Circuit Interrupter Including Improved Trip Circuit Using Current Transformers", issued June 18, 1974 to Shimp and U.S. Pat. No. 3,602,783, "Circuit Breaker Device Including Improved Overcurrent Protective Device", issued Aug. 31, 1971 to Engle, et al., all assigned to the assignee of the present invention. However, the above-mentioned patents do not generally provide loss of phase sensing as an integral part of a protective system requiring the use of added circutry or modules.
It is desirable to have a loss of phase sensing system which is an integral part of a load protection system. It is also desirable to have a loss of phase sensing system which will function when a load is operating at less than 100% of its capacity as well as 100% or slightly above of its rated capacity.